This invention relates to a multi-thread chain stitch sewing machine in which a spreader mechanism used to form upper decorative stitches is switched active and inactive, and to an over-edge chain stitch sewing machine in which a selecting operation is carried out so that upper decorative stitching is performed or not.
In general, an over lock sewing machine has upper and lower loopers, to perform over-edge chain stitching. Recently, as disclosed by Japanese Patent Application Laid-open No. 6-262 (corresponding to U.S. Pat. No. 5,255,622), an over look sewing mechanism has been known which has a mechanism for switching over operating and no-operating the upper looper so that either the over-edge chain stitch or the multi-thread chain stitch can be formed.
Alternately, as disclosed by Japanese Patent Application Laid-open No. Hei. 7-68072 filed by the present Applicant an over lock sewing machine has been known which has a mechanism for holding the upper looper, and a loop spreading mechanism with respect to the lower looper, so that over-edge chain stitching and lower decorative stitching (covering chain stitching) can be selectively performed.
In addition, as for an industrial sewing machine, an upper decorative stitch sewing machine is also known in the art which has a spreader to form upper decorative stitches only.
In the above-described lower decorative stitching operation, decorative stitches are formed on the lower surface of a fabric which confronts with the throat plate, and the feeding teeth of the sewing machine are protruded from the upper surface of the throat plate to feed the fabric. Hence, the lower surface of the fabric is rubbed by the feeding teeth, thus being damaged. Therefore, generally the fabric is placed over the throat plate in such a manner that the wrong side (back) of the fabric confronts with the throat plate accordingly with the feeding teeth. Hence, the lower decorative stitches are formed on the wrong side (back) of the fabric. And the wrong side of the fabric on which the decorative stitches have been formed must be set outside when for instance clothes are formed with the fabric. Hence, the resultant clothes are low in quality.
In the case of sewing a cloth material for which, as in the case of attaching rubber tape or lace to underwear, it is necessary to perform decorative stitching on both surfaces thereof (i.e., it is necessary to perform decorative stitching on each of the two surfaces), which makes it rather troublesome to perform the sewing operation.